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JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 17 
microscope range in size from three to six microns (.003 to .006 milli¬ 
meter) but much of the sulfur in a true hydrophilic colloidal solution is 
not within the range of visibility at such magnification. Very few par¬ 
ticles even of the size noted are visible. After the solution had stood for 
21 days, the range in size of particles was from 6 to 30 microns. At this 
stage precipitation of sulfur is very noticeable. Ground sulfur, 95 per 
cent of which would pass a 200-mesh sieve, showed a range in size of 8 
to 40 microns. 
Preparation of Colloidal Solutions 
Two methods were followed, (1) hydrophilic colloidal sulfur—made by 
passing hydrogen sulfid through a saturated solution of sulfur dioxid 
until the odor of the latter cannot be distinguished. The latter point is 
important, or if free sulfur dioxid remains in the solution, it is much more 
apt to burn foliage. Solutions made in this way gave approximately 3 
to 7 per cent sulfur by analysis. It will be seen in Table I that this is 
a very stable preparation in which the particles grow or aggregate 
but slowly. (2) The second method of preparation (hydrophobic 
colloidal sulfur) is by precipitating lime sulfur solution by adding 
concentrated hydrochloric or sulfuric acid. (Phosphoric acid offers 
some advantages but is more expensive.) The acid was added to the 
solution to a point of acidity as shown by methyl orange, it usually re¬ 
quiring about 0.5 cc. concentrated acid per 10 cc. of lime sulfur concen¬ 
trate (1.3° Baume). Such solutions show a tendency to aggregate sulfur 
particles up to the point of precipitation within a few days. The use of 
another colloid such as glue or gelatine delayed this especially if the 
glue solution was added before the acid. For commerical purposes add 
one pound of glue dissolved in water, to five gallons of lime sulfur solu¬ 
tion, then in addition, two to four pints of concentrated acid, or until the 
yellow color disappears and the solution is slightly acid to methyl 
orange. A larger amount of glue may be used if the material is supposed 
to stand several days after preparation and before being used. 
Properties of Collidal Solutions 
It will be seen from the data in Table I that it is possible to make 
colloidal solutions either with a sulfur dioxid solution or by precipitating 
a lime sulfur solution, with acids, that have such finely divided sulfur 
particles that they are invisible at a magnification of 80 times. Since it 
is generally accepted that minute particles of sulfur are more effective 
